Patent GB-865767-A (GB)
Title: Improvements in or relating to apparatus for electrostatically depositing liquid coating material
IPC: B05B5/053
Filed: 1957-03-20
Abstract: 865,767. Spray producers. RANSBURG, H. J., RANSBURG, H. G., RANSBURG, H. P., and RANSBURG, E. M., [trading as RANSBURG CO., HARPER, J.]. March 20, 1957 [March 20, 1956], No. 31139/60. Divided out of 865,763. Class 69 (3). A gun, for use in electrostatic spray painting, comprises a charging electrode, means presenting a current path to establish in use a high voltage on the electrode, the current path including a resistance high enough, and the electrode and any other exposed parts that in use are at high potential having an effective capacity low enough to ensure that if the electrode when at high voltage approaches an earthed object any resulting discharge is small enough to avoid fire hazard, or an objectionable electric shock or both. The effective capacity is a measure of the tendency of the electrode to contribute to such a discharge, and may be kept below the true electrostatic capacity by the use of a high distributed resistance over the electrode. As shown in Fig. 2, the gun 14 has a body with an outer housing 31 of polyethylene. At one end is a rotating bell-like head 16 of nylon, polyethylene or similar insulating material, having its inner surface coated with a layer 16c of a material having chemcial and mechanical resistance to the paint, and a high electrical resistance, e.g. an alkyd resin coating material containing finely divided carbon particles. The head is rotated by an electric motor (not shown) through a hollow flexible shaft 24 which passes through the flexible conduit 23 and into the body of the gun. The end of this shaft is connected, both mechanically and electrically with a hollow ceramic tube 29a with an outer casing 29b of high resistance material in a rigid carrier member 29c of synthetic resin material. The head 16 is mounted on the outer end of this member by rubber 0-rings. The conduit of the tube opens into the head at 16a, and the resistance layer 29b is connected with the layer 16c by a coating on the tip of tube 29a. Paint is supplied through the conduit in the hollow shaft 24 and tube 29a by means of a pump, not shown. The resistance layer 29b, and the paint inside the tube 29a form two resistances in parallel which together provide the necessary high resistance. The flexible conduit 23 has an outer sheath 25 of polyethylene which extends into the body of the gun, and is held in place by the enlarged portion 33 moulded into it. In an other embodiment, shown in Fig. 4, a gun has three separate connections 41, 42 and 43 at its rear, all brought together into a single flexible conduit assembly covered with an earthed flexible metallic outer sheath 44. A bell member 45 is mounted on a rotatable shaft 46 connected with a flexible drive shaft in the conduit 42. The bell is of non-conducting material, e.g. nylon, with a surface layer 47 of high-resistance material. High voltage is introduced through the electrical conduit 41 and passes through two fixed resistors 48 and 49, e.g. of 500 megohms each, to a small metal leaf spring 50 in rubbing contact with the resistive coating 47. Paint is supplied through the conduit 43 to the valve 54 operated by the trigger 51. A passageway 57 leads from the valve 54 to the hollow shaft 46, permitting paint to reach the bell and spread outwards to the edge 45a where it is charged and atomized. The valve 54 and handle 53 are both earthed. In use, the shaft 24 or the electrical conduit 41 is connected with one terminal of a power pack, the other terminal of which is earthed. The article to be coated is also earthed. Specifications 710,920, 865,764, 865,765, 865,766 and 865,768 are referred to.